ON Convoys - Slow Convoys

Slow Convoys

Until April 1943, ships capable of speeds between 9 and 13 knots were assigned to odd-numbered (fast) convoys—sometimes designated ON(F); while ships capable of speeds between 6 and 9 knots were assigned to even-numbered (slow) convoys—sometimes designated ON(S) or (ambiguously) ONS. This situation, which has proved confusing to modern historians, prevailed until a new and separate series of ONS (Outbound North Slow) convoys was organized. These convoys were sequentially numbered from ONS 1 sailing on 4 April 1943 to ONS 51 sailing on 21 May 1945. ON 171 was a fast convoy, as were all subsequent ON convoys. The ONS series were suspended in the summer of 1944 as escort groups were diverted to cover the Normandy landings. A total of 1873 ships sailed in 51 ONS convoys. Only 5 of these were attacked (around 10%), though two of these battles were of major significance; ONS 5 is regarded as the turning point of the campaign, while ONS 18 was the last major convoy battle in the campaign. Nineteen ships were lost (around 1%) from ONS convoys.